The term “Maillard reaction” and “Maillard reactants/products” are terms of art which define the complex series of chemical reactions between carbonyl and amino components derived from biological systems and the associated reactants and products, respectively. The term Maillard reaction is used herein in the established broad sense to refer to these reactions, and includes the closely associated reactions which are usually coupled with the Maillard reaction sensu stricto (such as Strecker degradation).
In foods, the Maillard reaction results in both the production of flavors and browning (see Bailey, M. E. (1994) Maillard reactions and meat flavor development, pages 153-173, In: Flavour of meat and meat products, Ed. F. Shahidi, Academic Press; Ames, J. M. (1992) The Maillard Reaction, pages 99-143, In: Biochemistry of Food Proteins, Ed. B. J. F. Hudson, Elsevier App. Sci. London).
With respect to flavor generation, the Maillard reaction can be broken down into four stages. The first stage involves the formation of glycosylamines. The second stage involves rearrangement of the glycosylamines to form Amadori and Heyns rearrangement products (often abbreviated in the literature to “ARPs” and “HRPs”, respectively). The third stage involves dehydration and or fission of the Amadori and Heyns rearrangement products to furan derivatives, reductones and other carbonyl compounds (which may have significant organoleptic qualities). (These “third stage products” may also be produced without the formation of ARP's or HRP's. The fourth stage involves the conversion of these furan derivatives, reductones and other carbonyl compounds into coloured and aroma/flavor compounds. Thus, products and reactants present in both the third and fourth stage of the Maillard reaction contribute towards aroma and or flavor.
Thus, the terms “Maillard reaction”, “Amadori rearrangement product”, “Heyns rearrangement product”, “aroma compound” and “flavor compound”, unless indicated otherwise, are used herein in the above-described senses.
Maillard reactions occur naturally in food, but it is also known to use Maillard reaction products to improve the flavor of foodstuffs.
Caramel and biscuit flavor generation has been described in many model reaction systems. 4-hydroxy-2,5-dimethyl-3(2H)-furanone (corresponding to Furaneol™ a registered trademark of Firmenich Inc.) is one compound associated with caramel flavor. 4-hydroxy-2,5-dimethyl-3(2H)-furanone can be produced in high levels from 6-deoxy-hexoses such as rhamnose (6deoxy-L-mannose), fucose (6-deoxy-L-galactose) and 6-deoxy-fructose by reaction with an amine (Wong et al. 1983, J Org Chem 48: 3493-3497; Whitehead 1998, Food Technology February 52: 40-46). Specifically, 4-hydroxy-2,5-dimethyl-3(2H)-furanone can be generated from a rhamnose and amine interaction by Amadori formation via the loss of an amine group, forming 2,3-enolization leading to a diketone, which leads to 4-hydroxy-2,5-dimethyl-3(2H)furanone after dehydration and cyclization (Pisarnitskii et al. 1992, Appl Biochem Microbiol 28: 97-100). At basic pH, 4-hydroxy-2,5-dimethyl-3(2H)-furanone can be generated from rhamnose alone, whereas under acidic conditions formation is only found in presence of an amino acid (e.g. arginine). The combination of rhamnose and arginine results in 4-hydroxy-2,5-dimethyl-3(2H)-furanone formation, which is 40-50 fold higher than any other sugar amine combination (Haleva-Toledo et al. 1997, J Agric Food Chem 45: 1314-1319; 1999, J Agric Food Chem 47: 4140-4145). Maximum 4-hydroxy-2,5-dimethyl-3(2H)-furanone generation is found at pH 8.0 with increasing temperature (90° C.) in aqueous buffers. Lower amount of 4-hydroxy-2,5-dimethyl-3(2H)-furanone can also be generated during base catalyzed fructose degradation (Shaw et al. 1968, J Agric Food Chem 16:979-982).
Amino acids as flavor precursors have been extensively studied in combination with reducing sugars in water or ethanol model Maillard reaction systems. Among the compounds known to be generated from proline and rhamnose are 4-hydroxy-2,5-dimethyl-3(2H)-furanone and several 2,3-dihydr(1H)-pyrrolizines (Shaw and Ho 1989, Thermal generation of aromas, eds. Parliament T H, McGorrin R J, Ho C-T, American Chemical Society, Washington, D.C.; Shaw et al. 1990, Perfumer & Flavorist 15: 60-66; Tressl et al. 1985, J Agric Food Chem 33: 919-923 and J Agric Food Chem 33: 934-928). As 4-hydroxy-2,5-dimethyl-3(2H)-furanone is thermally unstable, its concentration is strongly reduced at temperatures higher than 150° C. in model aqueous reaction systems. The biscuit/bready/roast flavor attributes have also been studied in many model systems. Proline was described by Hodge et al. (1972, Cereal Sci Today 17: 3440) as the key amino acid precursor for roast aroma. It was further shown by Schieberle (1990, Z Lebensm Unters Forsch 191: 206-209) that a key impact compound, 2-acetyl-1-pyrroline was generated from proline and ornithine. In U.S. Pat. No. 3,687,692 and U.S. Pat. No. 3,782,973 it was reported that proline-based reaction mixtures produced a caramel character upon heating with cyclic ketones. U.S. Pat. No. 4,022,920 disclosed that Amadori rearrangement compounds have been produced from proline and 6-deoxy-aldohexoses such as rhamnose under reflux in ethanol followed by drying. The dried mixture was incorporated into a food matrix followed by heating.
U.S. Pat. No. 4,940,592 is directed to a process wherein rhamnose is mixed with amino acids such as leucine, alanine, and phenylalanine in water or propylene glycol, coated onto uncooked foodstuff followed by microwave radiation. U.S. Pat. No. 5,041,296 also disclosed flavor precursors treated by microwave radiation before mixing with a foodstuff. EP 0 398 417B1 also disclosed reactions between rhamnose and proline in other non-fat systems such as water, ethanol, propylene glycol and glycerol.
WO0249452 discloses a process for the production of flavor concentrates comprising the addition of a mixture of flavor precursors comprising proline, ornithine or protein hydrolysate, and rhamnose, fructose or fucose, to a fat-based medium and heating the mixture to about 100-140 C for about 10-120 minutes.
However, there are problems associated with the introduction into baked foodstuffs of flavor active molecules generated by Maillard reactions.
The time taken to generate appreciable quantities of flavor active materials, for example by reacting amino acids and reducing sugars, is long relative to the baking times of many baked products. For example, in U.S. Pat. No. 4,022,920 example 1,6-deoxy-D-galactose and L-proline are refluxed in ethanol for 3 hours to generate flavorants. The flavor active reaction products, extracted into fat, are added to a shortcake dough and baked in example 9 of U.S. Pat. No. 4,022,920 rather than the un-reacted amino acid and reducing sugar.
If mixtures of flavor active molecules are added to ingredients which are then baked (e.g. in the production of wafer or extruded cereals), many desirable volatile flavor components are lost. This has a number of disadvantages. The desirable aromas/flavors associated with volatile compounds are only found in low levels in the finished product (having been lost during the preparation process). Moreover, many components of the finished flavor may be flashed off during cooking (so leading to loss from the flavor profile of important aroma volatiles). This is a particular problem in wafer baking as large volumes of steam are vented during the baking process which will carry away volatile and water soluble flavor active molecules. This has two major disadvantages as it removes flavor from the final product and leads to an unpleasant working environment around the ovens.
WO9962357 discloses flavor releasing compositions using micro emulsions where a flavor precursor is converted into an active flavor in the mouth. The increase in water activity activates an enzyme to convert the flavor precursor into a flavor. However, such compositions are not readily applied to ingredients which are baked to form baked foodstuffs. During baking the micro emulsions will be dehydrated and break down, and any enzymes will be denatured by the heat.
In baked goods that comprise other components, such as a chocolate coated wafer biscuit, it is possible to add flavor active molecules generated by reacting flavor precursors into the non baked component. However, consumers expect the desirable baked flavors to come from the baked component, and tasting these flavors in a different component such as the chocolate coating is undesirable as it can seem artificial to the consumer.